Instinct
by I saw the monster in you
Summary: "We need to stop this monster at all costs." "Even if the cost is you?" She didn't realize it, but his instincts were getting the best of him. To any other slayer, the reason was obvious, but will it be too late for Lucy to realize it herself? Will Natsu be able to see through his anger enough to remember what matters most? *Rated M for paranoia and future scenes*
1. What's the mission, Master?

**Hey guys! I thought I'd write you guys a Nalu with no strings attached since I know some of you are confused about "The Symposium." I apologize for the confusion, but if you're patient, everything will make sense soon enough in that story, I promise. I hope you guys enjoy this, and let me know what you think! I don't own the characters of Fairy Tail, though I wish I did.**

The doors of the guild slammed open, in tune with Lucy's ire.

"It wasn't a big deal Natsu!" Her companion strode in after her, a slight discoloration of his jaw apparent on the right side of his face. He glared lightly at the back of her head.

"I heard you scream, Lucy." She spun to give him the full force of her glare.

"I was in the _shower_!" She exclaimed. To the people in the guild, it was obvious enough with her still wet hair that was thrown up in a messy bun, and her thrown together outfit. This was also an argument that they had heard before, although there seemed to be something off about Natsu. Lucy was slightly unnerved of the intensity in Natsu's olive gaze. After a moment, the look passed, and he responded.

"I just reacted...it was instinct." The celestial mage watched Natsu for a moment, her chocolate gaze narrowed, before she sighed and walked away, heading over to her usual seat at the bar.

"And he just slammed the door open and tore back the curtain!"

"Sounds like the beginning of a chapter in _50 Shades of Gray_." Levy murmured, glancing at her best friend over the rim of her glass. Lucy's gaze snapped to the blunette, who nearly chocked on her drink from her friend's surprised and slightly angered expression. Lucy pursed her lips and glared good-naturedly at Levy.

"And you'd know this, why?" The response was blasé, but it caused Levy's face to turn red, up into the tips of her ears, making Lucy laugh. The blonde clutched her stomach from laughing so hard before trying to get her breathing under control. Hearing Natsu throwing insults with Gray, she sobered up a bit.

"But seriously...he has no concept of privacy." Levy shrugged.

"Well he is a creature of instinct." Lucy snorted rather unladylike.

"He's a creature alright." Her gaze fell back to her two friends brawling, just in time to catching Natsu breathing fire. _He's a dragon._

After Levy left her for a mission with team Shadowgear, Lucy went in search of someone who would be best for the other perspective.

"And you're over here, _why,_ blondie?" said blonde eyed the dragon slayer curiously.

"Have you ever...behaved like Natsu?" Gajeel snorted.

"As if. Salamander has the maturity of an 8 year old. The kid runs on instincts." Lucy frowned. There was that word again. Gajeel noticed, and scowled slightly. "What? Don't know what it means?"

"Of course I do," she stated distractedly. "a natural or intuitive way of acting or thinking." she spout off. There was a beat of silence before Gajeel chuckled lowly. The noise immediately caught Lucy's attention, causing her to frown again. _I'm gonna have frown lines by the time I'm 20._ "What?" she snapped. Gajeel smirked, his teeth menacing-looking.

"Maybe that's what it means for normal people, but what about dragons?"

"But the dragons left years ago." Lucy protested. Gajeel raised a studded eyebrow.

"Me, Wendy, and Salamander were raised by and _as_ dragons. We were taught their morals, their beliefs. _Our_ instinct...is that of a dragon's, a wild beast, a huge monster. Our instinct is that of an animal's, the basic human desires, because humans really only play themselves off as sophisticated beasts. We were raised as _predators._"

For the first time, since her lethal confrontation with Gajeel, she feared him. He truly terrified her when he put it that way, making things much more serious. _I mean...it's_ **_Natsu_** _we're talking about. Him? Raised as a predator? Unbelievable._ Gajeel could see the disbelief on her face, could smell the fear inkling into her scent, turning the normally sweet scent bitter. "And you've seen it yourself, bunny-girl." Confusion overtook her scent, and the older dragon slayer spoke again. "Every battle Salamander has had, it involves instinct; the way he moves, what he uses to attack, to defend. In no situation is a dragon prey. When we fight with such a narrow-minded focus, our instincts tell us to protect, to defend...to destroy." Lucy watched the red-eyed dragon in front of her.

"Of course...when it comes to nakama, Natsu always wants to protect them." Gajeel stood up, towering over the celestial mage, only adding to his intimidation.

"Not only protect."

"Lucy?" The blonde started at her own name, and looked up into the familiar blue eyes of Mirajane.

"Mira-san..." she smiled easily. "Was there something you needed?"

"The master was looking for you." Lucy nodded and stood up, walking upstairs. Worry flashed over the white-haired barmaid's face.

"What's bothering you, Lucy-chan?" she murmured.

After knocking, she only had to wait a moment.

"Come in Lucy." She opened the door, but when she saw Natsu, some of her original annoyance came back. Happy was standing on Makarov's desk, who must've seen the annoyance on her face, because he quickly spoke.

"I have a mission for you three."

"What's the mission, jii-san?" Natsu asked, excitement filling his voice. A seriousness covered Makarov.

"Around the town of Brunewell, teenage girls and young women are going missing, only to show up dead." Lucy gasped, her hand flying to her chest. Anger pulsed easily off of Natsu. "And most of them have been found raped." Lucy felt the temperature in the room skyrocket. She looked to her partner. He was completely rigid, his muscles tightening, his jaw clenching. His olive eyes had practically darkened to onyx. After making sure that neither of his children would speak, Makarov continued. "I have had three charms made to fit each one of you. It will change your physical appearance to everyone else but you three." Happy was given a collar, and his blue fur turned grey before flashing back to blue every time Lucy focused on him. Natsu was given a silver band that fit on his middle finger of his right hand. The dragon slayer had hair as black as Gajeel's, and piercing blue eyes. Only if she focused on him, could she see the pink hair and green eyes. Finally, Makarov gave her a gold necklace in the shape of a key. She watched her hair turn brown, before turning back into its golden color almost immediately.

"Umm...master, my necklace didn't work. My hair is the same." The old man smiled, and held up a mirror.

"Look for yourself." In it, Lucy saw a green-eyed brunette.

"Wow..." she mouthed. "And your marks have also been covered. This is a complete, undercover mission, and Lucy...you will be bait."

If she though Natsu was angry earlier, he was furious now. He turned on Makarov, blue eyes blazing like fire.

**"NO!"** he roared. Makarov's gaze narrowed.

"Lucy is a very capable mage. Besides, she has you, correct?" It only appeased the dragon slayer slightly. Before he could oppose again, Lucy spoke, turning to her best friend.

"Natsu, I need to do this." He looked at her, betrayal flashing over his features. "Think of all those girls who didn't have anyone to save them." She met his gaze unflinchingly, emerald orbs blazing. "I can save the ones yet to be taken!" Lucy bit her lip, lowering her voice to barely a whisper. "I can give closure to those we couldn't."

**So this is the beginning of my story. I don't believe that this will be as long as the others are going to, but then again, these stories have a mind of their own. Please, once again, leave reviews! :) **


	2. Burning Brunewell to the ground

**Onto chapter two! These three are finally onto the mission, arriving in Brunewell, but tempers are still raised. Will they be able to keep away from each others throats long enough to catch the culprit? Read and find out! (Wow, I sound corny. lol)**

Brunewell was almost as large as Magnolia. Lucy held Happy in her arms as they exited the train. Thanks to Wendy, Natsu had no trouble on the ride and once again, Lucy hesitated before speaking to him. She was walking close to him, and he glanced at her. Instead of his usual, wide grin, he scowled at her. Lucy's steps faltered and she frowned. _So he's still mad at me?_

"You can be mad all you want, this is the right thing to do." He just grunted, and continued to walk ahead of her. Lucy glared at the back of his head and tightened her hold on Happy. The now-grey cat frowned and patted Lucy's arm.

"Natsu means well Lucy. How do you think he feels?"

"What do you mean Happy?" She glanced down at the cat who was watching Natsu.

"I mean...Natsu's first instinct is to protect his nakama...but now he has to _willingly_ lose you. It's not something easy to come to terms with." The blonde bit her lip, her face looking thoughtful.

"You're right Happy...but he needs to understand that this is more than just me or him. We need to stop this _monster_ at all costs. Happy finally looked up at her, his onyx orbs solemn.

"Even if the cost is you?" he asked softly. Lucy thought for a moment.

"I would give up my life, to save hundreds of girls who don't have the power to save themselves. If you have power, you also have a duty." She felt Happy sigh.

"Lucy..." he almost sounded disappointed. "Natsu will burn Brunewell to the ground if you are hurt on this mission. And he will never forgive himself." Knowing the cat was right, Lucy could do nothing but follow after the annoyed, black-haired dragon slayer.

The two mages did not speak to one another until they had dropped their stuff off at the hotel and went in search of a place for lunch. Happy, tired of the uncomfortable atmosphere, stayed back at the hotel, relaxing. Once again, Lucy was quietly following after her partner, not paying much attention. Before she could look up to make she that they weren't hopelessly lost, someone ran into her. She grunted and fell back, feeling her hip come into contact with the cement.

"Oww..."she groaned. _Thank god I'm wearing shorts._

"My apologies." Lucy looked up to a blond-haired, brown-eyed young man. He at least looked sheepish. Lifting her hands off of the ground, she winced and looked at them. The skin of her palms was rubbed off and starting to bleed. Lucy hissed lightly, when a familiar voice spoke.

"What do you think you're doing?!" The voice growled darkly. The young man was shoved roughly out of the way, and tender hands grasped her wrists gently. Lucy slowly looked up to Natsu, frowning. He was focused on her hands before his cobalt gaze glanced up to hers.

"Are you okay Luce?" he murmured, his voice low. She nodded slowly, and he stood up, gently helping her to her feet while keeping her hands upturned. "Let's get you cleaned up." He protectively wrapped an arm around her back and shouldered the man out of the way. The guy stumbled, and Lucy could see that although there was anger on his face, he was smart enough to sense Natsu's power. The celestial mage said nothing, just let the dragon slayer lead her to a bathroom.

All cleaned up, and bandages on her hands, she sat next to Natsu at the countertop of a diner they had found. It was slightly busy, but Natsu had already ordered drinks. Lucy saw with slight surprise that he had ordered her her favorite, a chocolate milkshake.

"Thank you Natsu." He said nothing, just drank the golden liquid in his cup. The brunette sighed. She laid a bandaged hand over his own. "I'm sorry. I understand why you were so upset about me taking this mission, but you need to understand why I need to do this." She could see that although he wanted to continue ignoring her, he had glanced at her quickly from the corner of his eye. Lucy decided to forge on. She took a deep breath, letting it out slowly. "I've grown up pampered all my life. I've never had to lift a finger, wasn't allowed to. Before I came to Fairy Tail, I didn't know what it was like to be able to protect someone with your own power, but now?" Even though he tried not to, he was sucked in, finally looking at her. She smiled at him, placing her hand on top of his. "Now I do...and it's all thanks to you guys. So if can take what little power I have to protect others who don't have _any_...It's worth it." She smiled softly at him, and could see his ice-cold gaze warm and soften. He sighed loudly and took a gulp of his drink. He didn't look back at her, but Lucy heard him mutter a 'fine.'

After lunch, they decided to walk around for a bit, and get a feel of the place and tried to find the places the women were attacked and later on found. It made Lucy feel sick to her stomach to realize what had happened to these poor girls, with no one there to save them. Thanks to Makarov, their room was near the center of all the trouble so it would be easier for them to solve this quickly. This was one mission Lucy hoped didn't take long.

The brunette was walking ahead of Natsu, finding herself walking towards the market in the center of Brunewell. It was only two blocks from the hotel, which Lucy was thankful for, and had the best vendors. She watched Natsu's bright blue eyes light up before he went in search of more food. Lucy shook her head and snickered.

"That young man sure looks like he can put away." Her green eyes caught an older woman with a gentle smile. Lucy glanced back over her shoulder at her companion, to see him trying to stuff a whole shish-kebab in his mouth without stabbing himself on the stick. She nearly smacked herself on the forehead, but thought it was less harmful to talk to the woman. With a wide smile, she nodded.

"Yes he sure can." The older woman's brown eyes twinkled.

"Is he your boyfriend?" Lucy nearly choked on her spit, blinking owlishly.

"Wha-wait..._him?_" She went to point at Natsu over her shoulder, just to make sure that that was who the older woman was talking about, but he wasn't standing there anymore. Lucy frowned slightly but turned back to the woman who was still looking at her expectantly. She finally shook her head no. "I'm sorry to sound so impolite but definitely not!" She watched mirth swim in eyes similar to her own, and she felt a heavy but familiar arm drape itself across her shoulders.

"Ne, Luce, look what I found!" his left hand flourished a small bag full of white balls that were tied with a pink ribbon. "They're yogurt! You always have this stuff in your fridge but I wasn't sure if it was the same, so the woman let me try some, and it was!" He sounded so amazed that Lucy couldn't help but smile. She gently reached for the bag, glancing up to catch his eye.

"Thanks Natsu. That's very kind of you." He only grinned at her before he released her and went in search of something else. The brunette held the bag gently in her hands a small smile on her face.

"He seems like a good young man." Lucy looked up in surprise, having forgotten the woman. She smiled softly again and nodded.

"Yeah...he is."

The older woman watched the brunette girl in front of her with a smile on her own face. It was obvious how much that young man meant to her, even if she wasn't completely aware of how deeply it ran. She wouldn't tell her that, though. _Let her find that out on her own._ She couldn't help thinking with a slight chuckle. Curious green eyes looked up at her. She merely shook her head, a strand of grey hair coming loose from its bun. The girl blinked, her eyes back to its unclouded emerald and stuck her hand out. The older woman gave her own, smiling. The brunette nodded and grinned back.

"My name is Lucy. It was nice to meet you-?"

"Kokoa, child. It was a pleasure to meet you. Will you be in town awhile?" The brunette nodded, and waved as she took off in search for her male companion.

She found him talking to a vendor that was selling fish. Lucy immediately thought Happy, and scoffed good naturedly. She didn't say a word, just strolled up to stand next to him. Natsu was too absorbed to notice her, but the vendor smiled and held up a finger apologetically.

"I'll be right with you." Lucy only smiled, and waited for him to turn his back to them so he could help another customer. She turned to Natsu, about to yell at him, but he spoke.

"The people here are scared. There are no women out alone, and if they're out at all, they have someone else with them. And it's usually a guy." Lucy's mouth went slack as she quickly looked around to see that what Natsu was saying was true. There were mostly men out, and the women that were present had another male with them, or they were out as a group of girls. She quickly saved face and snorted softly.

"Of course they are. Someone here is killing their friends...their neighbors...their family. Wouldn't you be scared?" Natsu turned to her, his cobalt gaze darkening.

"I'd want to get to the bottom of it." Lucy placed her hands on her hips.

"Well that's what we're here for." he turned away from her, picking a fish and paying for it.

"Don't remind me." the dragon slayer grumbled.

Things were extremely tense in the celestial mage's hotel room when night fell. Lucy pulled her chestnut hair into a high ponytail, before curling the ends. She was wearing a black bodice that had a sweetheart neckline and buttoned up the front. A sliver of her skin was revealed between her top and pants, which were a deep blue, and tucked into her leather boots which were also black. She spun and looked at Happy.

"How do I look?" The grey cat begrudgingly complimented her, before curling up on her bed and watching her with worried eyes. Lucy caught the look and sat down on the bed next to him, sighing. "You know I'm going to be careful Happy, but I need to do this." She pet between his ears, and he let out a purr.

"Aye..." he murmured. She looked up at the doorway that connected her and Natsu's room. She really wished he wasn't so angry with her. "He can't fight his instincts, so he's going to fight the only other factor he can." Lucy groaned a little in the back of her throat.

"Which is me..."

"Aye."

**So next we'll get to see how the mission goes. Will this be easier than it looks? How will Natsu react? Please, as always, reviews are welcome!**


End file.
